JPS6380102A - Steam generator - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention partitions high-temperature fluid and low-temperature fluid with a partition wall.

In particular, it relates to a steam generator that transports thermal energy from a high-temperature side to a low-temperature side to heat and evaporate a fluid at a low-temperature side.

The present invention relates to a steam generator suitable for using liquid metal on the high temperature side and water on the low temperature side.

[Conventional technology]

In a liquid metal cooled fast breeder reactor, the heat generated in the reactor is transported to an intermediate heat exchanger using primary sodium. The sodium on the secondary side of the intermediate heat exchanger is further circulated and acts as the hot side fluid of the steam generator to generate steam.

The steam spins a turbine and generates electricity. The secondary sodium loop between the intermediate heat exchanger and the steam generator is designed to prevent the reactor from being affected even if a crack occurs in the heat transfer tube of the steam generator and a Na/water reaction occurs. It is provided.

However, the presence of the secondary sodium loop is one of the factors that increases the cost of fast breeder reactors. For this reason, in recent years, a system has been considered that eliminates the secondary system loop and directly leads the secondary system sodium to the steam generator. In this case, in order to prevent Na/water reaction in the steam generator,
As in the above known example, an amount of gas such as helium is provided between the sodium on the high temperature side and the water on the low temperature side.

[Problem that the invention seeks to solve]

Since the above-mentioned conventional technology provides an intermediate gas layer, the structure of the steam generator becomes complicated, and its contribution to cost reduction becomes small.

In addition, when water/sodium is flowed inside and outside the heat transfer tubes of the steam generator without providing an intermediate gas layer, the maintainability of the steam generator is expected to be lower than that of a steam generator without an intermediate gas layer. think of.

When a crack occurs in the heat transfer tube and sodium and water come into contact, a chemical reaction (exothermic reaction) occurs as shown in the following equation.

2Na+2HzC)42NaOH+HzAlong with the removal of the generated heat, an important problem is the inflow of the generated hydrogen gas into the reactor core. In a liquid metal cooled fast breeder reactor, when gas flows into the reactor core, nuclear fission reactions become more intense and the amount of heat generated increases rapidly.

An object of the present invention is to provide a steam generator having a structure in which even if a crack occurs in a heat transfer tube and a Na/water reaction occurs, the generated hydrogen gas does not flow out of the steam generator.

[Means for solving problems]

In a gas-liquid two-phase downward flow in which a mixture of gas and liquid flows downward in a vertical pipe, when the average flow velocity of the gas and liquid becomes small, the gas is affected by buoyancy and stops descending. Consider the gas-liquid two-phase downward flow shown in Figure 2.

Take the positive direction of the X-axis downward. The average flow velocity of the gas phase (gas) and liquid phase is j (m/s), and the flow velocity of the gas phase is Ug (m/s).
s ), the drift velocity of the gas phase V II 4(m
/s) is given by a linear equation when the distribution of the gas phase within the cross section of the flow path is -like.

V t J = U t j
(1) Although the gas phase distribution within the cross section of the flow path strictly depends on the flow state, a -like distribution is a sufficiently valid assumption.

To prevent the gas phase from falling.

Uz=VIIJ+J<O...(2). In the downward flow shown in Figure 2, Via<O, so the formula % formula % (3
) Therefore, if the condition of equation (3) is satisfied, the gas will rise in the opposite direction to the flow of the liquid phase. The drift speed depends on the density P1*Pf of the liquid phase and the gas phase and the surface tension 6, and is theoretically given by the following equation.

g is the gravitational acceleration. At low pressure, p m > p z, so equation (4) is.

As the temperature of the fluid increases, p decreases and vg
l tends to become large.

On the other hand, as shown in FIG.
In order to increase the amount of heat exchanged from sodium to water, it is necessary to make the area of the flow path within the tube as small as possible to increase the flow rate of sodium.

In the present invention, as shown in FIG. 3, the prevention of the leakage of hydrogen gas generated from the Na/water reaction when a crack occurs in the heat transfer tube from the steam generator (Ifii) 1 is as shown in FIG.
This is achieved by providing a region 9 in which the average flow velocity j is smaller than the drift velocity V ta on the downstream side of the drift velocity V ta .

[Effect]

The drift speed is calculated from equation (5) based on the minimum value of the Na temperature at the bottom of the heat transfer tube of the steam generator, including during steady operation and during accidents. For example, if the sodium temperature is 350°C
Then, Vt4=0.6 m/s. The volumetric flow rate of the temperature-side fluid in the steam generator, that is, sodium, is defined as Q(m
/s), and if the flow path area of the downflow region in Fig. 3 is A, the flow velocity j = -, and the downflow region of the flow path area where j < Vm- is the downstream side of the heat exchanger tube of the steam generator. If set at
The hydrogen gas generated during the water reaction is the flow of sodium.
It rises in the opposite direction and is collected above the free liquid level, preventing it from flowing into the core.

〔Example〕

A first embodiment of the present invention will be described below with reference to FIG.

The inside of Ml of the steam generator is partitioned into a shell 1 side and a heat exchanger tube 4 side by a tube plate 12. The barrel 1 has a barrel side inlet nozzle 2. Outlet nozzle 3. An inlet nozzle 5 and an outlet nozzle 6 are provided on the heat exchanger tube side. Outside the mI side outlet nozzle 3 is a gas separation tank 9 with an upflow wall 8 and a free liquid level. Furthermore, the gas separation tank 9 is equipped with a gas pressure regulating valve 11 that also serves as a hydrogen gas discharge and an outlet nozzle 10. The support plate 7 prevents the heat exchanger tube 4 from vibrating. In the downward flow region of the gas separation tank 9, the flow path area is set large so that the flow velocity j of sodium is smaller than the drift velocity. High-temperature sodium from the reactor core passes through the shell-side inlet nozzle 2 and descends inside the shell, heating and evaporating water in the heat transfer tubes 4. The cooled sodium passes through the outlet nozzle 3, rises along the upward flow wall 8, flows into the gas separation tank 9, becomes a downward flow, and returns to the reactor through the outlet nozzle 10. Water from the turbine condenser is passed through the heat transfer tube side inlet nozzle 5 to the heat transfer tube 4.
According to this embodiment, the water rises inside the water, becomes water vapor, and flows out from the outlet nozzle 6 to the turbine.

During steady operation, the flow rate of sodium in the shell 1 outside the heat exchanger tubes 4 is sufficiently high, and steam can be efficiently generated. Furthermore, even if a crack occurs in the heat exchanger tube 4 and a Na/water reaction occurs and hydrogen gas is generated, the gas separation tank 9
This has the effect of completely separating in the downflow region of the reactor and preventing it from flowing into the reactor core.

A second embodiment of the present invention will be explained with reference to FIG.

In this embodiment, the inlet nozzle 2 on the shell side is arranged at the bottom and the outlet nozzle 3 at the upper part, and after the sodium rises inside the shell and exits the outlet nozzle 3, it immediately becomes a downward flow. By keeping the flow path area of the gas separation tank the same as in the first embodiment, it is possible to prevent the hydrogen generated due to the Na/water reaction from flowing out, and with a simple structure, the entire steam generator can be made smaller than in the first embodiment. can be converted into

A third embodiment of the present invention will be explained with reference to FIG.

In this embodiment, the inlet/outlet nozzles 5 and 6 on the heat exchanger tube side are provided at the lower part of the shell 1, and the heat exchanger tube side flow path is separated into an inlet side and an outlet side by a partition plate 13. Water or steam is W! Make a U-turn at the top of 41.

A fourth embodiment of the present invention will be explained with reference to FIG.

In this embodiment, the gas separation tank 9 is connected to the downstream side of the shell-side outlet nozzle by a pipe 14, and the maintainability of the steam generator can be maintained as before.

A fifth embodiment of the present invention will be explained with reference to FIG.

A hydrogen gas detector 15 is installed in the gas space of the gas separation tank 9, and a heater 16 that is activated by a hydrogen gas detection signal is installed in the sodium tank 9. When hydrogen gas is detected and the heater is activated, the temperature of the sodium in the tank rises and the density p becomes smaller.

Therefore, as is clear from equation (4), the drift speed of hydrogen gas increases, the rising speed of hydrogen gas increases, and the reliability of gas separation increases.

〔Effect of the invention〕

According to the present invention, even if a Na/water reaction occurs in the steam generator in a fast breeder reactor in which the sodium secondary system loop has been removed, the generated hydrogen gas can in principle be separated 100% from the sodium. It is possible to prevent a situation where gas flows into the reactor core and the amount of heat generated in the reactor core increases rapidly.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a steam generator according to an embodiment of the present invention, FIG. Figure 4. 5, 6 and 7 are longitudinal sectional views of other embodiments of the invention. 1... Steam generation hull, 2... Shell side inlet nozzle.

Claims (1)

[Claims] 1. In a steam generator consisting of a shell, a heat transfer tube, and a tube plate, a downward flow region having a free liquid level is provided downstream of an outlet nozzle for fluid flowing on the shell side. Characteristic steam generator. 2. The steam generator according to claim 1, wherein the flow velocity in the downward flow region is lower than that in the shell. 3. The steam generator according to claim 1, wherein the downward flow region is constituted by a container surrounding the body of the steam generator. 4. In claim 3, the flow velocity in the container surrounding the shell is set to be equal to or lower than the drift velocity determined by the density and surface tension of the liquid metal sodium flowing on the shell side, and the density and gravitational acceleration of hydrogen gas. A steam generator characterized by: 5. Claim 4, wherein the flow path cross-sectional area of the downward flow region in the container is equal to or larger than a value obtained by dividing the volumetric flow rate of the liquid metal sodium flowing through the body side by the drift speed. A steam generator characterized by: 6. The steam generator according to claim 1, wherein the downward flow region is constituted by a container provided on the descending side of the body side fluid outlet nozzle. 7. The steam generator according to claim 6, wherein the flow velocity within the container is set to be equal to or lower than the drift velocity. 8. In claim 6, the flow path cross-sectional area of the downward flow region in the container is set to be equal to or larger than a value obtained by dividing the volumetric flow rate of the liquid metal sodium flowing through the body side by the drift speed. A steam generator characterized by: